There's a growing interest in what our genes say about our health. And in recent years, quite a few companies have sprung up to help us listen with the help of personalized DNA tests.

For a few hundred dollars and a vial of spit, these companies will search your DNA for sequences that predict your physical traits, your response to certain drugs and your risk for any number of diseases.

One such company, California-based 23andMe, is attempting to use the data to do something different: search for new genes linked to Parkinson's disease. The company, which calls itself the world's first genetics-based social network, has collected more than 125,000 DNA samples from customers.

Most customers likely wanted to find out more about their personal genetic risks — not to contribute to medical science. But in 2009, the company decided to do genetic research, and it invited anyone diagnosed with Parkinson's disease to donate their DNA sample.

23andMe recruited people online using social media, and at Parkinson's research conferences. In exchange for participating, they're offered the company's personalized genetics services free. Participants provided a DNA sample and answered questions about their diagnosis, symptoms and lifestyle habits in online surveys.

"They may in theory be able to involve 10,000 people with Parkinson's disease, and do it cheaply and easily," explains Hank Greely, a Stanford Law School professor who follows genetics companies. "Now that's something that academic researchers would love to be able to do."

In the past, researchers looked at families with many members who had the disease, allowing them to zero in on single genes that would dramatically increase a person's risk of getting Parkinson's. But of the million or so people in the U.S. with Parkinson's disease, less than 10 percent have any of the genes discovered so far.

Researchers think that's because there are many genes involved in Parkinson's — but that their effects are too small to be seen in just a few hundred to a few thousand people. Emily Drabant, research director at 23andMe, hopes that by looking at many thousands of people, they may be able to find them.

"We know that there are many genes, so the idea is when you aggregate across many thousands of people you can start to see genes that have perhaps a small effect on risk for Parkinson's," she says. "Perhaps, you have three or four risk variants and the combination increases your risk for Parkinson's quite significantly."

But observers like Greely say a dose of skepticism is in order. He wonders if 23andMe's customers will truly be representative of the population, and if the subjects can be trusted to accurately report their diagnosis and symptoms.

Criticism of direct-to-consumer genetics companies is nothing new. Many have questioned the ethics of delivering genetic information directly to the consumer, as well as the value and the accuracy of the genetic risks they report.

23andMe is now seeking FDA approval for its genetic testing kits. The company submitted applications for seven health-related tests so far and plans to include more than 100 more in the coming months.

When it comes to research, many also wonder if these companies will have incentives to report positive findings too soon. But Robert Green of Harvard Medical School says that companies with large profit incentives have been doing medical research for years, and while skepticism is in order, the controversial nature of these companies is not a reason to entirely discredit their approach to research.

"You know social media has changed the rest of our lives – there's no reason why social media and the Internet can't revolutionize some aspects of medical research as well," he says. "I see this as part of a larger trend, not something that's really restricted to genetic testing companies."

23andMe has had considerable success. Though short of its goal, the company has discovered two new genes. Drabant says they have also been able to uncover rare combinations of mutated genes associated with Parkinson's that no one had found before.

Drabant says she recognizes an Internet-based approach to genetics research makes many scientists uncomfortable. It's something new. But she also says she believes companies like 23andMe have the power to make important genetic discoveries faster, and cheaper than has been done in the past. Given enough time and research subjects, she hopes to prove it.

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.